1. Field of the Invention
The present invention relates to a process for the treatment of aqueous liquid effluents containing organic and inorganic matter for the purpose of their beneficiation. It relates more specifically to a process for the treatment of aqueous liquid effluents containing organic and inorganic matter so as to obtain, on the one hand, a purified aqueous liquid phase and, on the other hand, a solid organic agricultural fertilizer and/or soil improver.
It also relates to the application of the said process to the treatment of liquid animal excreta and in particular of animal manure, especially pig manure.
It also relates to the application of this process to the treatment of other effluents, such as the effluents coming from agri-foodstuffs industries.
In general, the present invention relates to a process for the treatment of an aqueous liquid effluent containing organic and inorganic matter having a content of from 1 to 12% by weight of dry matter.
2. Description of the Related Art
Considerable production of aqueous effluents of agricultural origin, especially of animal manure, poses problems of increasing seriousness to agriculture and also to protection of the environment, especially of water courses and ground-water tables. Increasingly stringent regulations are being put into place so as to avoid the very negative effects of pollution of the environment due to various types of animal manure.
The pollution caused affects the entire environment: air, water, soil (ground water). More specifically, the pollution is manifested by:
unpleasant smells (volatile organic matter, H.sub.2 S, NH.sub.3); PA1 discharge of nitrates (into surface water and ground water); PA1 discharge of phosphates (essentially into surface water by entrainment during run-off); and PA1 the bacteriological aspect (when spreading or transporting manure). PA1 subjecting the effluent to one or more primary liquid/solid separation steps and, optionally, one or more physico-chemical treatment steps, thereby obtaining, on the one hand, a liquid medium containing no more than 3% and preferably no more than 1% and especially no more than 0.7% by weight of dry matter and having a turbidity of at most 300 NTU, preferably at most 200 NTU and in particular at most 120 NTU and, on the other hand, a collection of concentrates containing in total at least 15% and preferably at least 20% by weight of dry matter; PA1 subjecting the liquid medium thus obtained to an ultrafiltration or microfiltration step, thereby obtaining an ultrafiltrate or microfiltrate containing at most 1% by weight of dry matter and having a turbidity of at most 100 NTU and preferably at most 50 NTU; PA1 subjecting the ultrafiltrate or microfiltrate to a reverse osmosis operation, thereby obtaining a concentrate and a permeate, this permeate constituting the purified aqueous phase; PA1 optionally, adding and mixing with the collection of concentrates an organic complement in particulate form so as to obtain a mixture containing from 20 to 40% by weight of dry matter, and PA1 aerobically fermenting (or composting) the said mixture until an organic soil improver and/or organic fertilizer having a dry matter content of 40 to 60% by weight is/are obtained.
At the present time, the known processes for purifying such effluents have the drawback of not always treating the problem in its entirety. For example, the biological processes of the nitrification/denitrification type produce a biological sludge containing most of the phosphates, it being possible for this sludge to be used in a correct agronomic manner only in spreading over surfaces equivalent to that of a raw manure. The same applies to the processes of extraction and thermal dehydration of volatile organic matter and of ammoniacal nitrogen compounds. Systems combining the biological processes of anaerobic digestion and of thermal dehydration using the biogas give rise to complex units operating on a very large scale. They then require a collective treatment centre and take up a lot of room on the roads. Moreover, they are a factor in contagion from one stock farm to another, requiring strict sanitary operations to be carried out on the transportation means.
The purpose of the present invention is to solve the abovementioned drawbacks. To this end, the present invention aims to provide a process for the treatment of aqueous effluents containing organic and inorganic matter, which allows all these effluents to be utilized on the very sites of their production or in their vicinity without any appreciable pollution transfer.